In Japanese Patent Application Laid-open (kokai) Pub. No. H10-70856, an invention is disclosed which relates to a constant-voltage induction feeding apparatus using a saturable reactor. This is an apparatus for supplying driving electric power to a vehicle running along a track, from the track to the vehicle in a non-contact manner using electromagnetic induction. The induction incoming circuit mounted on the vehicle comprises, as its basic structure, a receiving coil for generating an induced electromotive force when it is placed in an alternating field (at a constant frequency of approximately 10 kHz) generated by an equipment associated with the track, a resonance capacitor connected with the receiving coil and forming a resonance circuit tuned at the frequency of the magnetic field, and a converter for rectifying AC power extracted from the resonance circuit and providing it to a load such as a motor.
In the case of this induction incoming circuit, when the load consumes little power (referred to as “light-load state”), the circuit is broken because the induced voltage of the receiving coil is increased without any limitation as far as any restrictive factor does not work. Therefore, the above prior art employs a structure in which any abnormal increase of the voltage is regulated, i.e., the voltage is maintained constant, by connecting in parallel a saturable reactor with the resonance circuit formed by the receiving coil and the capacitor.
The inventors have continued studying further the various characteristics that a nonlinear reactor suitable for the above purpose should have. In case of a saturable reactor to be used in a high-frequency region of 10 KHz or higher, there is an advantage that the eddy-current loss heating caused by the high-frequency magnetic field is small when the core is formed of ferrite presenting a characteristic of high resistance. However, since ferrite considerably changes its magnetic characteristic (a saturation magnetic flux density) according to its temperature, there is a problem that the above-described constant voltage characteristic provided by the saturable reactor is not stable when the temperature fluctuation of the environment where the reactor is used is large.
Since an amorphous alloy soft magnetic material and a nanocrystal soft magnetic material show a stable magnetic characteristic against temperature fluctuation, there is an advantage that the constant voltage characteristic is stable even if the temperature fluctuation of the environment where the reactor is used is large when a saturable reactor having a core formed of such a material is used. However, when the core is formed of this kind of material by winding the material shaped in a strip, there is a problem that an eddy-current tends to be generated on the surface of the strip when a steep pulse current flows in the coil and, thereby, the core itself is heated remarkably.
For either core material, in the structure in which the saturable reactor is connected with the above-described induction incoming circuit for maintaining the voltage constant, the core becomes magnetically saturated in the vicinity of the peak of each half wave of a high frequency of 10 KHz or higher in an operation mode effecting an action of maintaining the voltage constant and, therefore, a steep pulse current flows in the coil wound around the core (thereby, any voltage increase is regulated). As known, this kind of steep high-frequency pulse current has a serious problem that it gives hazardous electromagnetic interference (EMI) to the surroundings.
The present invention was conceived in light of the above technical considerations. The object of the invention is to provide a composite core nonlinear reactor capable of stably suppressing any voltage increase without generating any steep pulse current and of alleviating its heating and its EMI problem, and to provide an induction incoming circuit using such a reactor.